I actually have a 3.8 '98 lesabre... I blew a radiator hose a couple days ago so I flushed my coolant system yesterday, and replaced my thermostat. well when i finished i did a test start and i let it run at idle for about ten minutes. well it is running about 210 degrees the overflow resivior is bubble'n and the radiator fan is staying on. a couple mistakes I made that which i noticed in hine site are... after I installed the new thermostat I took a good look at the old one and noticed a rubber O ring on the old thermostat. meaning I installed a thermostat without an O ring, plus I accidentally put a little extra coolant in the resivior (30 or 40 oz's). I also notice my intake manifold bolts where only finger tight, so i tightened the ones i could get too. #1 do i need that O ring? if so do i need a regular gasket and sealant for the therm. housing? #2 what are the consiquences of over filling your coolant system? #3 what do you recomend i do about the whole intake issue?

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Sounds like your water pump may be not working, while vehicle is off try squeezing both upper and lower radiator hose you should be able to feel the fluid in the lines and the hose should feel firm and not squish all the way together. Make sure you used the right coolant orange vs green and mix ratio. after all this has been confirmed start vehicle and squeeze hoses again before they get to hot to make sure the fluid is moving and now hoses should be pretty hard to squeeze at all while the truck is running. if you don't feel movement of fluids or hoses are very squishy it could be a vacuum leak and worst case your water pump, hope this helps-

aluminum radiator
plastic top and base seal
tanks held in with crimps on aluminum radiator

find a local radiator shop to replace top seal and top plastic part
of that radiator
not as expensive as a new radiator

replace the thermostat

pressure is too much on that crack for any diy repair product

pop off hose at the wrong time =cook the motor

Yes, it could be a few issues, I always believe to go the cheapest route first, so you are not just replacing parts to be replacing, Based on your description, Normally it would not be overflowing if your pump is not working, It could be a clogged hose, you would have to flush system to see if that was the case, but based on my feeling, i believe it is a stuck thermostat, If your tank is overflowing, it would have to be a main hose block, but i don't believe that is the case, i would have thermostat replaced, to confirm that, for a around 50 bucks (if you stay away from dealer) you can have the radiator flushed, which is a good idea anyway, then you will know for sure it is the thermostat, and they can put that in after they flush it, or you can put thermostat in, pick there brain, when they flush it, and they can point where it is, it is just a couple of bolts to take off, clean gasket area, replace with new gasket, after of course taking old thermostat out and replacing with new one.

I hope this helps you, (again, i think it is thermostat that is stuck) thanks Mike from fixya

if your radiator has a cap remove it and start the motor turn the heater on high and put it on defrost watch the coolant when the bubbles stop coming out and the fluid is at a full level there should be no more air in the system. a miss fire is caused by bad plugs or plug wires and i would back flush the heater core remover the hoses going to the firewall and flush the heater core with water from your garden hose. to check the water pump start the motor and watch the pump to see if any fluid comes from it.

Top radiator hose moves coolant away from engine and through radiator and bottom hose moves it into the engine

Its best to replace radiator. You can purchase a flush kit from Auto Zone and back flush the system ( meaning go against the normal flow of coolant with a garden hose). But Rust usually means Radiator seen better days and you don't want this stuff causing problems around the head.

Build up in the coolant system a faulty Sensor reporting that the engine is hot when it is not. You can try running a coolant flush through the system to remove that possible problem. If you are basing this overheating problem on coolant being forced out the over flow, do a compression check on the cylinders. If one or more of the cylinders is running extremely high compression you may have a faulty head gasket, cracked head or cracked block.

When engine is cold, remove the bottom radiator hose from the radiator and let all fluid drain into a bucket.
Replace hose and refill cooling system with desired inhibitor/coolant mix.